/*
 * Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */


package org.graalvm.compiler.loop;

import static java.lang.Math.abs;
import static org.graalvm.compiler.loop.MathUtil.unsignedDivBefore;
import static org.graalvm.compiler.nodes.calc.BinaryArithmeticNode.add;
import static org.graalvm.compiler.nodes.calc.BinaryArithmeticNode.sub;

import org.graalvm.compiler.core.common.type.IntegerStamp;
import org.graalvm.compiler.core.common.type.Stamp;
import org.graalvm.compiler.core.common.util.UnsignedLong;
import org.graalvm.compiler.debug.DebugCloseable;
import org.graalvm.compiler.loop.InductionVariable.Direction;
import org.graalvm.compiler.nodes.AbstractBeginNode;
import org.graalvm.compiler.nodes.ConstantNode;
import org.graalvm.compiler.nodes.GuardNode;
import org.graalvm.compiler.nodes.IfNode;
import org.graalvm.compiler.nodes.LogicNode;
import org.graalvm.compiler.nodes.NodeView;
import org.graalvm.compiler.nodes.StructuredGraph;
import org.graalvm.compiler.nodes.ValueNode;
import org.graalvm.compiler.nodes.calc.ConditionalNode;
import org.graalvm.compiler.nodes.calc.NegateNode;
import org.graalvm.compiler.nodes.extended.GuardingNode;
import org.graalvm.compiler.nodes.util.IntegerHelper;
import org.graalvm.compiler.nodes.util.SignedIntegerHelper;
import org.graalvm.compiler.nodes.util.UnsignedIntegerHelper;

import jdk.vm.ci.meta.DeoptimizationAction;
import jdk.vm.ci.meta.DeoptimizationReason;
import jdk.vm.ci.meta.SpeculationLog;

public class CountedLoopInfo {

    private final LoopEx loop;
    private InductionVariable iv;
    private ValueNode end;
    private boolean oneOff;
    private AbstractBeginNode body;
    private IfNode ifNode;
    private final boolean unsigned;

    CountedLoopInfo(LoopEx loop, InductionVariable iv, IfNode ifNode, ValueNode end, boolean oneOff, AbstractBeginNode body, boolean unsigned) {
        assert iv.direction() != null;
        this.loop = loop;
        this.iv = iv;
        this.end = end;
        this.oneOff = oneOff;
        this.body = body;
        this.ifNode = ifNode;
        this.unsigned = unsigned;
    }

    
Returns a node that computes the maximum trip count of this loop. That is the trip count of this loop assuming it is not exited by an other exit than the 
count check. This count is exact if isExactTripCount() returns true. THIS VALUE SHOULD BE TREATED AS UNSIGNED. /**
     * Returns a node that computes the maximum trip count of this loop. That is the trip count of
     * this loop assuming it is not exited by an other exit than the {@linkplain #getLimitTest()
     * count check}.
     *
     * This count is exact if {@link #isExactTripCount()} returns true.
     *
     * THIS VALUE SHOULD BE TREATED AS UNSIGNED.
     */
    public ValueNode maxTripCountNode() {
        return maxTripCountNode(false);
    }

    public boolean isUnsignedCheck() {
        return this.unsigned;
    }

    
Returns a node that computes the maximum trip count of this loop. That is the trip count of this loop assuming it is not exited by an other exit than the 
count check. This count is exact if isExactTripCount() returns true. THIS VALUE SHOULD BE TREATED AS UNSIGNED. 
Params:
assumeLoopEntered – if true the check that the loop is entered at all will be omitted./**
     * Returns a node that computes the maximum trip count of this loop. That is the trip count of
     * this loop assuming it is not exited by an other exit than the {@linkplain #getLimitTest()
     * count check}.
     *
     * This count is exact if {@link #isExactTripCount()} returns true.
     *
     * THIS VALUE SHOULD BE TREATED AS UNSIGNED.
     *
     * @param assumeLoopEntered if true the check that the loop is entered at all will be omitted.
     */
    public ValueNode maxTripCountNode(boolean assumeLoopEntered) {
        StructuredGraph graph = iv.valueNode().graph();
        Stamp stamp = iv.valueNode().stamp(NodeView.DEFAULT);

        ValueNode max;
        ValueNode min;
        ValueNode absStride;
        if (iv.direction() == Direction.Up) {
            absStride = iv.strideNode();
            max = end;
            min = iv.initNode();
        } else {
            assert iv.direction() == Direction.Down;
            absStride = NegateNode.create(iv.strideNode(), NodeView.DEFAULT);
            max = iv.initNode();
            min = end;
        }
        ValueNode range = sub(max, min);

        ConstantNode one = ConstantNode.forIntegerStamp(stamp, 1, graph);
        if (oneOff) {
            range = add(range, one);
        }
        // round-away-from-zero divison: (range + stride -/+ 1) / stride
        ValueNode denominator = add(graph, range, sub(absStride, one), NodeView.DEFAULT);
        ValueNode div = unsignedDivBefore(graph, loop.entryPoint(), denominator, absStride, null);

        if (assumeLoopEntered) {
            return graph.addOrUniqueWithInputs(div);
        }
        ConstantNode zero = ConstantNode.forIntegerStamp(stamp, 0, graph);
        // This check is "wide": it looks like min <= max
        // That's OK even if the loop is strict (`!isLimitIncluded()`)
        // because in this case, `div` will be zero when min == max
        LogicNode noEntryCheck = getCounterIntegerHelper().createCompareNode(max, min, NodeView.DEFAULT);
        return graph.addOrUniqueWithInputs(ConditionalNode.create(noEntryCheck, zero, div, NodeView.DEFAULT));
    }

    
Determine if the loop might be entered. Returns false if we can tell statically that the loop cannot be entered; returns true if the loop might possibly be entered, including in the case where we cannot be sure statically. 
Returns:
false if the loop can definitely not be entered, true otherwise/**
     * Determine if the loop might be entered. Returns {@code false} if we can tell statically that
     * the loop cannot be entered; returns {@code true} if the loop might possibly be entered,
     * including in the case where we cannot be sure statically.
     *
     * @return false if the loop can definitely not be entered, true otherwise
     */
    public boolean loopMightBeEntered() {
        Stamp stamp = iv.valueNode().stamp(NodeView.DEFAULT);
        StructuredGraph graph = iv.valueNode().graph();

        ValueNode max;
        ValueNode min;
        if (iv.direction() == Direction.Up) {
            max = end;
            min = iv.initNode();
        } else {
            assert iv.direction() == Direction.Down;
            max = iv.initNode();
            min = end;
        }
        if (oneOff) {
            max = add(graph, max, ConstantNode.forIntegerStamp(stamp, 1), NodeView.DEFAULT);
        }

        LogicNode entryCheck = getCounterIntegerHelper().createCompareNode(min, max, NodeView.DEFAULT);
        if (entryCheck.isContradiction()) {
            // We can definitely not enter this loop.
            return false;
        } else {
            // We don't know for sure that the loop can't be entered, so assume it can.
            return true;
        }
    }

    
Returns:
true if the loop has constant bounds./**
     * @return true if the loop has constant bounds.
     */
    public boolean isConstantMaxTripCount() {
        return end instanceof ConstantNode && iv.isConstantInit() && iv.isConstantStride();
    }

    public UnsignedLong constantMaxTripCount() {
        assert isConstantMaxTripCount();
        return new UnsignedLong(rawConstantMaxTripCount());
    }

    
Compute the raw value of the trip count for this loop. THIS IS AN UNSIGNED VALUE;
/**
     * Compute the raw value of the trip count for this loop. THIS IS AN UNSIGNED VALUE;
     */
    private long rawConstantMaxTripCount() {
        assert iv.direction() != null;
        long endValue = end.asJavaConstant().asLong();
        long initValue = iv.constantInit();
        long range;
        long absStride;
        IntegerHelper helper = getCounterIntegerHelper(64);
        if (iv.direction() == Direction.Up) {
            if (helper.compare(endValue, initValue) < 0) {
                return 0;
            }
            range = endValue - iv.constantInit();
            absStride = iv.constantStride();
        } else {
            assert iv.direction() == Direction.Down;
            if (helper.compare(initValue, endValue) < 0) {
                return 0;
            }
            range = iv.constantInit() - endValue;
            absStride = -iv.constantStride();
        }
        if (oneOff) {
            range += 1;
        }
        long denominator = range + absStride - 1;
        return Long.divideUnsigned(denominator, absStride);
    }

    public IntegerHelper getCounterIntegerHelper() {
        IntegerStamp stamp = (IntegerStamp) iv.valueNode().stamp(NodeView.DEFAULT);
        return getCounterIntegerHelper(stamp.getBits());
    }

    public IntegerHelper getCounterIntegerHelper(int bits) {
        IntegerHelper helper;
        if (isUnsignedCheck()) {
            helper = new UnsignedIntegerHelper(bits);
        } else {
            helper = new SignedIntegerHelper(bits);
        }
        return helper;
    }

    public boolean isExactTripCount() {
        return loop.loop().getNaturalExits().size() == 1;
    }

    public ValueNode exactTripCountNode() {
        assert isExactTripCount();
        return maxTripCountNode();
    }

    public boolean isConstantExactTripCount() {
        assert isExactTripCount();
        return isConstantMaxTripCount();
    }

    public UnsignedLong constantExactTripCount() {
        assert isExactTripCount();
        return constantMaxTripCount();
    }

    @Override
    public String toString() {
        return "iv=" + iv + " until " + end + (oneOff ? iv.direction() == Direction.Up ? "+1" : "-1" : "");
    }

    public ValueNode getLimit() {
        return end;
    }

    public IfNode getLimitTest() {
        return ifNode;
    }

    public ValueNode getStart() {
        return iv.initNode();
    }

    public boolean isLimitIncluded() {
        return oneOff;
    }

    public AbstractBeginNode getBody() {
        return body;
    }

    public AbstractBeginNode getCountedExit() {
        if (getLimitTest().trueSuccessor() == getBody()) {
            return getLimitTest().falseSuccessor();
        } else {
            assert getLimitTest().falseSuccessor() == getBody();
            return getLimitTest().trueSuccessor();
        }
    }

    public Direction getDirection() {
        return iv.direction();
    }

    public InductionVariable getCounter() {
        return iv;
    }

    public GuardingNode getOverFlowGuard() {
        return loop.loopBegin().getOverflowGuard();
    }

    public boolean counterNeverOverflows() {
        if (iv.isConstantStride() && abs(iv.constantStride()) == 1) {
            return true;
        }
        IntegerStamp endStamp = (IntegerStamp) end.stamp(NodeView.DEFAULT);
        ValueNode strideNode = iv.strideNode();
        IntegerStamp strideStamp = (IntegerStamp) strideNode.stamp(NodeView.DEFAULT);
        IntegerHelper integerHelper = getCounterIntegerHelper();
        if (getDirection() == Direction.Up) {
            long max = integerHelper.maxValue();
            return integerHelper.compare(endStamp.upperBound(), max - (strideStamp.upperBound() - 1) - (oneOff ? 1 : 0)) <= 0;
        } else if (getDirection() == Direction.Down) {
            long min = integerHelper.minValue();
            return integerHelper.compare(min + (1 - strideStamp.lowerBound()) + (oneOff ? 1 : 0), endStamp.lowerBound()) <= 0;
        }
        return false;
    }

    @SuppressWarnings("try")
    public GuardingNode createOverFlowGuard() {
        GuardingNode overflowGuard = getOverFlowGuard();
        if (overflowGuard != null || counterNeverOverflows()) {
            return overflowGuard;
        }
        try (DebugCloseable position = loop.loopBegin().withNodeSourcePosition()) {
            IntegerStamp stamp = (IntegerStamp) iv.valueNode().stamp(NodeView.DEFAULT);
            IntegerHelper integerHelper = getCounterIntegerHelper();
            StructuredGraph graph = iv.valueNode().graph();
            LogicNode cond; // we use a negated guard with a < condition to achieve a >=
            ConstantNode one = ConstantNode.forIntegerStamp(stamp, 1, graph);
            if (iv.direction() == Direction.Up) {
                ValueNode v1 = sub(ConstantNode.forIntegerStamp(stamp, integerHelper.maxValue()), sub(iv.strideNode(), one));
                if (oneOff) {
                    v1 = sub(v1, one);
                }
                cond = graph.addOrUniqueWithInputs(integerHelper.createCompareNode(v1, end, NodeView.DEFAULT));
            } else {
                assert iv.direction() == Direction.Down;
                ValueNode v1 = add(ConstantNode.forIntegerStamp(stamp, integerHelper.minValue()), sub(one, iv.strideNode()));
                if (oneOff) {
                    v1 = add(v1, one);
                }
                cond = graph.addOrUniqueWithInputs(integerHelper.createCompareNode(end, v1, NodeView.DEFAULT));
            }
            assert graph.getGuardsStage().allowsFloatingGuards();
            overflowGuard = graph.unique(new GuardNode(cond, AbstractBeginNode.prevBegin(loop.entryPoint()), DeoptimizationReason.LoopLimitCheck, DeoptimizationAction.InvalidateRecompile, true,
                            SpeculationLog.NO_SPECULATION, null)); // TODO gd: use speculation
            loop.loopBegin().setOverflowGuard(overflowGuard);
            return overflowGuard;
        }
    }

    public IntegerStamp getStamp() {
        return (IntegerStamp) iv.valueNode().stamp(NodeView.DEFAULT);
    }
}